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a technology of phase measurement and system, applied in the field of system and method for phase measurement, can solve the problems of limited use of such techniques, inability to implement, and method cannot be fixed on a slab of material, and achieve the effect of efficient light gathering
Inactive Publication Date: 2005-05-19
MASSACHUSETTS INST OF TECH
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[0023] Another aspect of the present invention includes a fiber optic probe for optically imaging a sample, having a housing with a proximal end and a distal end, a fiber collimator in the proximal end of the housing coupled to a light source; and a graded index lens in the distal end of the housing, the lens having a first and second surface wherein the first surface is the reference surface and wherein numer...
Problems solved by technology
However, most such techniques are limited by an issue which is widely known in the filed at 2π ambiguity or integer ambiguity which can be defined as the difficulty in telling the interference fringes of an axial scan apart from each other.
While such a measurement approach works well in a controlled environment, it can hardly be implemented in a situation where there is less manipulability in the sample.
For example, the method does not work on a fixed slab of material which one is constrained to keep whole.
The problem lies in the fact that unmodified LCI is unable to tell the interference fringes of an axial scan apart from each other, described herein as the 2π ambiguity issue.
It is a problem that plagues most phase-based optical interferometric techniques.
As a result, these techniques are unabl...
Method used
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example 1
Phase Imaging of a Calibrated Sample
[0320] In this example, a well calibrated sample has been investigated and illustrates that the present invention can provide quantitative information at the nanometer (nm) scale. The sample consisted of metal deposition on a glass substrate, followed by etching. The metal deposit pattern was in the shape of the numeral eight and the thickness of the metal layer was about 140 nm, as measured with a nano-profilometer.
[0321]FIGS. 60A-60D show images obtained at four different phase shifts δ for a system using a reflection geometry. FIG. 60A is an image 2000 for δ=0; FIG. 60B is an image 2200 for δ=π; FIG. 60C is an image 2400 for δ=π / 2; and FIG. 60D is an image 2600 for δ=3π / 2.
[0322]FIG. 61 schematically illustrates a relationship 2100 between the electric field E vector 2102 and the high frequency wave vector component of the field, EH, and the low frequency wave vector component of the field, EL. As illustrated in FIG. 61, the y-axis 2110 a...
example 2
Phase Imaging of a Phase Grating
[0326]FIG. 64 shows a phase image 2400 of a phase grating with grooves nominally 10 microns wide and nominally 266 nm deep that was obtained using a transmission geometry. In FIG. 64 the z-axis 2402 is in units of nm and the y-axis 2404 and x-axis 2406 are in the units of CCD pixels. The vertical scale bar 2408 is also in units of nm and is provided to further facilitate determining depth (z-axis dimension) from the phase image 2400.
example 3
Phase Imaging of Onion Cells
[0327] In this example, onion cells were phase imaged using a transmission geometry in accordance with the present invention. An intensity image 2500 of the onion cells is shown in FIG. 65 for comparison to a phase image 2550 shown in FIG. 65. In both FIGS. 65 and 66 the y-axes 2502, 2552 and x-axes 2504, 2554 are in units of CCD pixels. The scale bar 2556 in FIG. 66 is in units of nm.
[0328] The intensity image, FIG. 65, represents the first acquired frame where there is no phase shift between the low and high frequency components δ=0. As shown by a comparison of FIGS. 65 and 66, a regular microscope (intensity) image has a very low contrast relative to the phase image obtained in accordance with the present invention. As seen in FIG. 66, the contrast is greatly enhanced in the phase image, where much finer structure of the cell can be distinguished. In addition, the information in the phase image is quantitative to a nanometer level precision and can b...
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Abstract
Preferred embodiments of the present invention are directed to systems for phase measurement which address the problem of phase noise using combinations of a number of strategies including, but not limited to, common-path interferometry, phase referencing, active stabilization and differential measurement. Embodiment are directed to optical devices for imaging small biological objects with light. These embodiments can be applied to the fields of, for example, cellular physiology and neuroscience. These preferred embodiments are based on principles of phase measurements and imaging technologies. The scientific motivation for using phase measurements and imaging technologies is derived from, for example, cellular biology at the sub-micron level which can include, without limitation, imaging origins of dysplasia, cellular communication, neuronal transmission and implementation of the genetic code. The structure and dynamics of sub-cellular constituents cannot be currently studied in their native state using the existing methods and technologies including, for example, x-ray and neutron scattering. In contrast, light based techniques with nanometer resolution enable the cellular machinery to be studied in its native state. Thus, preferred embodiments of the present invention include systems based on principles of interferometry and/or phase measurements and are used to study cellular physiology. These systems include principles of low coherence interferometry (LCI) using optical interferometers to measure phase, or light scattering spectroscopy (LSS) wherein interference within the cellular components themselves is used, or in the alternative the principles of LCI and LSS can be combined to result in systems of the present invention.
Description
CROSS REFERENCES TO RELATED APPLICATIONS [0001] The present application is a continuation-in-part of U.S. patent application Ser. No. 10 / 823,389, filed Apr. 13, 2004, which is a continuation-in-part of U.S. patent application Ser. No. 10 / 024,455, filed Dec. 18, 2001, and claims the benefit of U.S. Provisional Application No. 60 / 479,732, filed Jun. 19, 2003. The entire contents of the above applications are incorporated herein by reference in their entirety.GOVERNMENT SUPPORT [0002] The invention was supported, in whole or in part, by a Grant No. P41-RR02594 from the National Institutes for Health. The Government has certain rights in the invention.BACKGROUND OF THE INVENTION [0003] Phase-based optical interferometric techniques are widely employed in optical distance measurements in which sub-wavelength distance sensitivity is required. Optical distance is defined as the product of the refractive index and the length. However, most such techniques are limited by an issue which is wi...
Claims
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